This invention relates to an electric power driven toothbrush with an electric motor disposed in a handle section and driving, through a driving mechanism and a translating device driven thereby, in an oscillatory manner a rotary toothbrush section, in which the driving mechanism is configured as a four-bar linkage including a crank adapted to be driven by means of the electric motor, the crank driving in an oscillatory manner at least indirectly a drive shaft of the toothbrush section by a means of a link and through a rocker.
A toothbrush of this type is already known from CH 384539 A. For one thing, however, the special configuration of the crank mechanism disclosed therein involves a large size which is undesirable in particular for toothbrushes. The crank is of the overhung type, that is, supported at only one end, involving an additional increase in size. For another thing, the crank bearing is subjected to major wear during operation of the toothbrush. Moreover, in this configuration of crank mechanism which is encapsulated in the housing to protect it from external influence, the problem exists of supplying the bearings with sufficient lubricating agents.
A further electric power driven toothbrush is known from EP 0 054 043 B1. Through an output shaft and a planetary gear train, the electric motor drives a toothbrush section drive shaft arranged in a sleeve-type shank. For this purpose, the drive shaft has at its output end an eccentrically disposed pin which is rotated by the drive shaft and is guided in a slotted guide of a drive member for the toothbrush section, the axis of which intersects angularly the axis of the drive shaft. The revolving motion of the pin causes rotation in alternating direction or oscillation of the drive member for the toothbrush section. Such a conversion of the rotary motion of the electric motor into an oscillating motion of the brush section allows, however, only a very small angle of rotation, because the slotted guide should be at a correspondingly large distance from the axis of the rotation of the toothbrush section for reducing the frictional resistances. The more closely the slotted guide approaches the axis of rotation of the toothbrush section, the higher become the frictional resistances, thus also increasing the noise developing in the operation of the toothbrush. The relatively large frictional resistance of the pin guided in the slotted guide also produces significant wear, resulting in a relatively short service life of the driving elements.